import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;

/**
 * @auther: Alessio
 * @date: 2021/1/12
 * 题目：实现一个自旋锁
 * 自旋锁好处：循环比较获取知道成功为止，没有类似wait的阻塞
 *
 * 通过CAS操作完成自旋锁，A线程先进来调用myLock方法自己持有锁5秒钟，B随后进来后发现
 * 当前有线程持有锁，不是null，所有只能通过自旋等待，知道A释放锁后B随后抢到。
 */
public class SpinLockDemo {

    //原子引用线程
    AtomicReference<Thread> atomicReference = new AtomicReference<>();
    public void myLock(){
        Thread thread=Thread.currentThread();
        System.out.println(Thread.currentThread().getName()+"\t come in");
        while (!atomicReference.compareAndSet(null,thread)){

        }
    }

    public void myUnLock(){
        Thread thread=Thread.currentThread();
        System.out.println(Thread.currentThread().getName()+"\t invoke myUnLock()");
        atomicReference.compareAndSet(thread,null);
    }

    public static void main(String[] args) {
        SpinLockDemo spinLockDemo = new SpinLockDemo();
        new Thread(()->{
            spinLockDemo.myLock();
            try {TimeUnit.SECONDS.sleep(5);} catch (InterruptedException e) {e.printStackTrace();}
            spinLockDemo.myUnLock();
        },"AA").start();

        try {TimeUnit.SECONDS.sleep(1);} catch (InterruptedException e) {e.printStackTrace();}
        new Thread(()->{
            spinLockDemo.myLock();
            try {TimeUnit.SECONDS.sleep(1);} catch (InterruptedException e) {e.printStackTrace();}
            spinLockDemo.myUnLock();
        },"BB").start();
    }
}
